Apparatus for continuously forming plastic sheet and corrugating with vacuum pressure

ABSTRACT

An apparatus for forming an extruded plastic sheet with vacuum pressure and without mating dies. The plastic sheet is extruded onto a heated portion of a supporting bed which maintains the sheet in a soft condition. The bed also includes a cooled portion adjacent to the heated portion with a plurality of parallel grooves which extend continuously through the cooled portion and at least partially through the heated portion. A vacuum pressure is provided within the grooves between the bed and sheet thereby pulling the sheet downwardly into the grooves. The residual heat within the sheet is then removed by the cooled portion of the bed to maintain the formed condition of the heated sheet. Various means are provided to maintain the vacuum pressure between the bed and sheet.

United States Patent Erlewine et al. June 3, 1975 [54] APPARATUS FORllvlegkl ii Y M] T C IS a 6 rs fi 3,709,647 1/1973 Barnhart 425/224VACUUM PRESSURE Primary ExaminerAndrew R. .luhasz [75] Inventors:Richard H. Erlewine; Charles W. A i tan ExaminerDavid B. Smith Richter,III; Arthur J. Calpha, Jr-, Attorney, Agent, or Firm-Woodard, Weikart,ll Of r Ernhardt & Naughton [73] Assignee: General Plastics Corporation,

Marion, lnd. [57] ABSTRACT An apparatus for forming an extruded plasticsheet [22] Filed 1973 with vacuum pressure and without mating dies. The[21] App1.No.: 350,727 plastic sheet is extruded onto a heated portionof a supporting bed which maintains the sheet in a soft condition. Thebed also includes a cooled portion adg gi ifigg jacent to the heatedportion with a plurality of parallel 58] Fie'ld 224 336 grooves whichextend continuously through the cooled 425/374 325 264/90 d portion andat least partially through the heated por- 'tion. A vacuum pressure isprovided within the grooves between the bed and sheet thereby pullingthe [56] References Cited sheet downwardly into the grooves. Theresidual heat UNITED STATES PATENTS within the sheet is then removed bythe cooled portion 3,024,496 3/1962 Colombo 425/384 X of the bed tmaintain the formed condition of the 3,071J30 1/ 1963 l e1 425/359 xheated sheet. Various means are provided to maintain 3 32 ii the vacuumpressure between the bed and sheet. 3:226:457 12/ I965 Smith 264/90 5Claims, 6 Drawing Figures l9 /23 '4 u f 22 'l O O o 4 i )li' q I l 1 l ol 24 I l o 1 'llpl I r 1 1 l Ill r l (I n i l 1 APPARATUS FORCONTINUOUSLY FORMING PLASTIC SHEET AND CORRUGATING WITH VACUUM PRESSUREBACKGROUND OF THE INVENTION 1. Field of the Invention This invention isin the field of sheet forming devices.

2. Description of the Prior Art A representative sample of the prior artis disclosed in the following US. Pat. Nos.: 2,238,534 issued to A.McDonald; 2,989,780 issued to S. S. Zimmerman; 3,179,726 issued to W. M.Perry; 3,273,203 issued to F. A Ross; and 3,640,666 issued to B. T.Jope, et al.

None of the prior art devices provide a high production capability whichmay be achieved by immediately forming a plastic sheet which moves ontothe forming device immediately from the extruder. By allowing immediateformation of the desired configuration of the sheet as the sheet passesfrom the extruder, intermediate steps are eliminated with the resultthat a continuous in line forming is achieved. Traditional forming diesare expensive to produce and to maintain. The invention disclosed hereinprovides for the formation of the sheet through the use of vacuumpressure without requiring mating forming dies.

By initially extruding a flat plastic sheet, it is also possible betweenthe extruder and the forming bed to laminate a printed overlay film(such as a wood grain pattern of printing) of material onto the extrudedsheet prior to the subsequent forming operation.

SUMMARY OF THE INVENTION One embodiment of the present invention ismethod of forming grooves in a sheet of plastic comprising the steps ofheating the sheet of plastic, moving the sheet of plastic while in aheated condition along a support having grooves thereon, and withdrawingduring the moving step air from the grooves of the support creating avacuum pressure between the sheet and the support and forcing the sheetinto the grooves of the support to form grooves in the sheet.

Another embodiment of the present invention is an apparatus forproducing grooves in a sheet of plastic comprising a supporting bed forreceiving the sheet including a heated portion and an adjacent cooledportion, the bed further including a top surface with a plurality ofridges and grooves formed on the top surface extending through thelength of the cooled portion and at least partially through the lengthof the heated portion, the bed having holes extending through the topsurface in the grooves to facilitate air removal, heating means operableto controllably heat the heated portion to maintain the sheet in a softcondition, cooling means operable to controllably cool the cooledportion for the cooling and hardening of the sheet, and air meansoperable to withdraw air through the holes in the bed creating a vacuumin the grooves of the bed between the sheet and the bed forcing thesheet into the grooves of the bed.

It is an object of the present invention to provide a method forcontinuously forming extruded sheet.

A further object of the present invention is to provide an apparatus forcontinuously forming extruded sheet.

In addition, it is an object of the present invention to provide amethod and apparatus for forming an extruded plastic sheet with vacuumpressure.

Related objects and advantages of the present invention will be apparentfrom the following description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of an apparatusincorporating the present invention.

FIG. 2 is a fragmentary enlarged view of that portion of the apparatusof FIG. 1 between the sheeter die and the powered pull rolls.

FIG. 3 is an enlarged top view of the supporting bed looking in thedirection of arrows 3-3 of FIG. 2

FIG. 4 is a cross sectional view taken along the line 4-4 of FIG. 3 andviewed in the direction of the arrows.

FIG. 5 is a cross sectional view taken along the line 5-5 of FIG. 3 andviewed in the direction of the arrows.

FIG. 6 is a cross sectional view taken along the line 6-6 of FIG. 3 andviewed in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT For the purpose of promoting anunderstanding of the principles of the invention, reference will now bemade to the embodiment illustrated in the drawings and specific languagewill be used to describe the same. It will nevertheless be understoodthat no limitation of the scope of the invention is thereby intended,such alternations and further modifications in the illustrated device,and such further applications of the principles of the invention asillustrated therein being contemplated as would normally occur to oneskilled in the art to which the invention relates.

Referring now more particularly to FIGS. 1 and 2, there is shown anapparatus 10 for forming grooves into a sheet 11 of plastic which iscontinuously extruded by extruder 12. Plastic granules are placed intothe hopper 13 of extruder 12 with sheet 11 then moving out of sheeterdie 14 in the direction of arrow 15.

A uniform hot melt of plastic at an approximate temperature of 400 F.emerges from extruder 12 into the sheeter die 14 and onto a continuouslymoving heated haul-off roll 16 which is rotatably mounted to frame 17. Asecond roll 18 is rotatably mounted to frame 17 and may be used tolaminate an overlay film 19 which extends downwardly from roll 20 so asto be contacted against sheet 11 by laminating roll 18. Roll 16 isvariable in speed as are the pair of powered pull rolls 21 and 22 whichare rotatably mounted to frame 23. Rolls 16, 21 and 22 are synchronizedso as to move sheet 11 across bed 24 at the appropriate speed. Bycontrolling the heating of roll 16, a skin will be imparted to sheet 11with sufficient heat retained in the sheet to permit subsequent thermalforming of the sheet by vacuum provided on bed 24.

Bed 24 includes a heated portion 25, a cooled portion 26 and an aftsupporting portion 27. The top surface 28 of bed 24 is provided with aplurality of ridges 29 and grooves 30 which extend through the length ofthe aft supporting portion 27 and through the length of the jcocooledportion 26. The ridges and grooves extend only through a portion of thelength of the heated portion 25. In the embodiment shown in FIG. 4,ridges 29 include a horizontal top surface 3] with a pair of divergingsurfaces 32 and 33 which extend downwardly to the bottom surfaces 34 ofthe grooves. The height of each ridge 29 is the distance betweensurfaces 31 and 34 and is constant through the length of the aft supporting portion 27 and the cooled portion 26; however, the height of eachridge decreases through the length of heated portion until top surfaces31 are blended into surfaces 34 at a location behind the leading edgeportion 35' (FIG. 3). As a result, as the hot sheet passes from roller16 onto the upwardly sloping heated portion 25, the sheet maintainscontact across the width of the leading edge portion 35' and is thenconveyed upwardly by the upward sloping surfaces 31 of ridges 29. Thesmooth and hot leading edge portion 35' allows for an airtight sealbetween the sheet and heated portion 25.

A plurality of holes 35 extend through surfaces 34 of each groove 30.Holes 35 are located at the junctions of surfaces 34 and the upwardsloping surfaces 32 and 33. Cooled portion 26 includes a vacuum chamber36 (FIG. 4) which is in communication with holes 35. Chamber 36 isconnected to a suitable vacuum producing device. Thus, as the heatedsheet moves along the top surfaces 31 of ridges 29, a vacuum is producedwithin chamber 36 thereby sucking the sheet downwardly into grooves soas to produce complemen tary sized grooves in the sheet.

A plurality of passages 37 extend immediately beneath surfaces 31 and 34and receive circulating cooled liquid. A means such as a pump isutilized to circulate the cooled liquid through passages 37. Likewise, aplurality of passages 38 extend beneath surfaces 31 and 34 in the heatedportion 25. Passages 38 are not connected to passages 37 and instead areconnected to a suitable source of heated liquid which in turn circulatesthe heated liquid through passages 38 thereby heating portion 26.

Bed 24 includes a pair of longitudinally extending edge portions 39 and40 with the ridges and grooves positioned therebetween. The top surfacesof edge portions 39 and 40 have a plurality of apertures 41 extendingtherethrough which are connected to the vacuum chamber 36. Air iswithdrawn through apertures 41 so as to suck the sheet downwardlyagainst edge portions 39 and 40 to effect an airtight seal between themoving sheet and edge portions 39 and 40. This airtight seal incooperation with the airtight seal existing between the sheet and thesmooth leading edge portion prevents air from escaping into the grooveseither from the front edge of the bed or either side of the bed. As willbe described later in this specification, a plurality of wheels forcethe formed sheet against surfaces 34 of the groove at the aft supportingportion 27 thereby preventing escape of air into the grooves from therear portion of the bed.

A pair of slots 50 and 51 (FIG. 3) are provided in edge portions and 39.Slots and 51 extend the length of bed 24 with the exception of theleading edge portion 35. The slots are positioned inwardly of apertures41. A pair of rollers 52 and 53 are rotatably mounted above heatedportion 25 with each roller having a circumferentially extending ridgewhich is received by the slots. For example, roller 53 has acircumferentially extending ridge 54 (FIG. 5) which extends into slot51. The sheet passes between the bed and rollers 52 and 53 with theridges on the rollers forc ing a portion of the sheet downwardly intoslots 50 and 51 thereby slidably locking the sheet to the bed as thesheet moves through the length of the bed. The portion of the sheetforced downwardly into slots 50 and 51 may then be subsequently severedfrom the main body of the sheet subsequent to the final forming of thesheet.

A plurality of rotatably mounted wheels 55 are mounted to axle 56 whichis rotatably mounted above supporting portion 27 of bed 24. Suitablemeans are provided to control the vertical movement of axle 56. As aresult, wheels 55 may be positioned downwardly into grooves 30 therebyforcing the formed sheet against surface 34 (FIG. 4). Thus, escape ofair into the grooves from the aft section of the bed is preventedthereby ensuring the integrity of the vacuum existing within the groovesbetween the bed and sheet.

As previously explained, as the extruded sheet moves continuously overthe bed, sufficient vacuum must exist between the bed and sheet so as toprovide continuous thermal forming of the sheet as it. is pulleddownstream over the bed. The cooled portion of the bed contains both thecontrolled vacuum and the liquid chill. The vacuum existing betweencooled portion 26 and the sheet travels up to the heated portion 25where it is sealed off by the action of the heat controlled doctor bar60 (FIG. 2) which is directly in front of the heated portion 25 andunder which the sheet must travel to effect the vacuum seal at theleading edge of heated portion 25. Doctor bar 60 (FIG. 1) is lower inelevation than the top surface of bed 24 thereby forcing the sheetdownwardly as it passes from roll 17 onto heated portion 25. As thesheet moves over heated portion 25, the peripheral edges of the sheetare locked and sealed to the top surface of the heated portion 25 toprevent the action of the vacuum from drawing the sheet inwardly in sucha manner so as to break the vacuum seal. As discussed, the slots areprovided on both sides of the bed to receive the rotatably mountedridged wheels to effect a sea] at the peripheral edges of the sheet andprevent any change in width of the sheet. The cooled portion 26 must besufficiently cool so as to remove residual heat from the sheet duringits total contact period with the cooled portion and at a sufficientrate to lower the temperature of the sheet to below the distortiontemperature of the resin (approximately F.) so that the sheet willretain the profile shape thereafter during its transportationdownstream. Precise control of the vacuum pressure between the sheet andbed is important to prevent total lockup of the sheet at the heatedportion and at the cooled portion. A high degree of chill capacity isessential to maximize production rate.

Many variations of the present invention are contemplated and includedherein although not shown. For example, in one embodiment, trim knivesare mounted downstream of the rotatably mounted wheels 55 to remove theperipheral edge portions of the sheets and to trim continuously thedesired width of panel. The powered pull rolls 21 and 22 (FIG. 1) mustmove the sheet at a continuous synchronized speed with roll 16 and withsufficient frictional action on the formed sheet so as to overcome thefrictional effect of the vacuum pressure exerted against the panel atthe heated portion and cooled portion. Eventually, the continuouslyformed sheet is moved past a cutoff saw table and trimmed to lengthautomatically by action of a limit switch.

The method of forming the grooves in a sheet of plastic includesextruding the sheet of material and then heating the extruded sheet. Theheating of the sheet occurs when the sheet is supported by the bed withthe sheet then moving along the bed which withdraws air from between thesheet and bed thereby forcing the sheet into grooves in the bed.Longitudinally extending edges of the sheet are contacted against thebed to effect an airtight seal therebetween during the moving of thesheet and during the creation of the vacuum pressure between the sheetand bed. The forward portion of the bed is continuously contacted acrossthe width of the sheet to effect an airtight seal therebetween. Thesheet is subsequently cooled.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

The invention claimed is:

1. An apparatus for producing grooves in a sheet of plastic comprising:

a supporting bed for receiving said sheet including a heated portion andan adjacent cooled portion, said bed further including a top surfacewith a plurality of ridges and grooves formed on said top surfaceextending through the length of said cooled portion and at leastpartially through the length of said heated portion, said bed havingholes extending through said top surface in said grooves to facilitateair removal;

heating means operable to controllably heat said heated portion tomaintain said sheet in a soft condition;

cooling means operable to controllably cool said cooled portion for thecooling and hardening of said sheet;

air means operable to withdraw air through said holes in said bedcreating a vacuum in said grooves of said bed between said sheet andsaid bed forcing said sheet into said grooves of said bed;

said bed including a pair of longitudinally extending edge portions withsaid ridges and grooves posi tioned therebetween, said edge portionshaving top surfaces with passages extending therethrough connected tosaid air means which is operable to withdraw air through said passageseffecting an airtight seal between said edge portions and said sheetmoving thereon and further comprising:

said edge portions each having a slot extending the length thereof; and

pressure means projecting into said slot with said sheet forced betweensaid pressure means and said slot.

2. The apparatus of claim 1 wherein said heating means includes passagesextending through said bed with heated fluid circulated therethrough,said cooling means includes passages extending through said bed withcoolant extending therethrough.

3. The apparatus of claim 1 wherein each groove is positioned betweentwo of said ridges with each groove having a bottom flat wall and withsaid ridges having diverging walls extending upwardly and outwardly fromsaid bottom flat wall, said holes to facilitate air removal are locatedat opposite longitudinal extending edge portions of said flat bottomwall adjacent said diverging walls.

4. An apparatus for producing grooves in a sheet of plastic comprising:

a supporting bed for receiving said sheet including a heated portion andan adjacent cooled portion, said bed further including a top surfacewith a plurality of ridges and grooves formed on said top surfaceextending through the length of said cooled portion and at leastpartially through the length of said heated portion, said bed havingholes extending through said top surface in said grooves to facilitateair removal;

heating means operable to controllably heat said heated portion tomaintain said sheet in a soft condition;

cooling means operable to controllably cool said cooled portion for thecooling and hardening of said sheet; and,

air means operable to withdraw air through said holes in said bedcreating a vacuum in said grooves of said bed between said sheet andsaid bed forcing said sheet into said grooves of said bed;

said ridges having a constant height on said cooled portion and adecreasing height on said heating portion, said heated portion having asmooth leading edge portion with said ridges blended smoothly into saidleading edge portion;

said sheet being extruded and conveyed onto said heated portion;

said bed including a pair of longitudinally extending edge portions withsaid ridges and grooves positioned therebetween, said edge portionshaving top surfaces with passages extending therethrough connected tosaid air means which is operable to withdraw air through said passageseffecting an airtight seal between said edge portions and said sheetmoving thereon and further comprising:

means operable to contact said sheet and move said sheet along thelength of said bed;

said edge portions each having a slot extending the length thereof andfurther comprising:

a pair of rollers rotatably mounted over said bed with said rollers eachhaving a circumferential ridge extending into said slot with said sheetforced between each roller ridge and each slot.

5. The apparatus of claim 4 and further comprising:

a plurality of rotatably mounted wheels aft of said heated portion andextending into said grooves to force said sheet against said bed andeffect an airtight seal therebetween.

1. An apparatus for producing grooves in a sheet of plastic comprising:a supporting bed for receiving said sheet including a heated portion andan adjacent cooled portion, said bed further including a top surfacewith a plurality of ridges and grooves formed on said top surfaceextending through the length of said cooled portion and at leastpartially through the length of said heated portion, said bed havingholes extending through said top surface in said grooves to facilitateair removal; heating means operable to controllably heat said heatedportion to maintain said sheet in a soft condition; cooling meansoperable to controllably cool said cooled portion for the cooling andhardening of said sheet; air means operable to withdraw air through saidholes in said bed creating a vacuum in said grooves of said bed betweensaid sheet and said bed forcing said sheet into said grooves of saidbed; said bed including a pair of longitudinally extending edge portionswith said ridges and grooves positioned therebetween, said edge portionshaving top surfaces with passages extending therethrough connected tosaid air means which is operable to withdraw air through said passageseffecting an airtight seal between said edge portions and said sheetmoving thereon and further comprising: said edge portions each having aslot extending the length thereof; and pressure means projecting intosaid slot with said sheet forced between said pressure means and saidslot.
 1. An apparatus for producing grooves in a sheet of plasticcomprising: a supporting bed for receiving said sheet including a heatedportion and an adjacent cooled portion, said bed further including a topsurface with a plurality of ridges and grooves formed on said topsurface extending through the length of said cooled portion and at leastpartially through the length of said heated portion, said bed havingholes extending through said top surface in said grooves to facilitateair removal; heating means operable to controllably heat said heatedportion to maintain said sheet in a soft condition; cooling meansoperable to controllably cool said cooled portion for the cooling andhardening of said sheet; air means operable to withdraw air through saidholes in said bed creating a vacuum in said grooves of said bed betweensaid sheet and said bed forcing said sheet into said grooves of saidbed; said bed including a pair of longitudinally extending edge portionswith said ridges and grooves positioned therebetween, said edge portionshaving top surfaces with passages extending therethrough connected tosaid air means which is operable to withdraw air through said passageseffecting an airtight seal between said edge portions and said sheetmoving thereon and further comprising: said edge portions each having aslot extending the length thereof; and pressure means projecting intosaid slot with said sheet forced between said pressure means and saidslot.
 2. The apparatus of claim 1 wherein said heating means includespassages extending through said bed with heated fluid circulatedtherethrough, said cooling means includes passages extending throughsaid bed with coolant extending therethrough.
 3. The apparatus of claim1 wherein each groove is positioned between two of said ridges with eachgroove having a bottom flat wall and with said ridges having divergingwalls extending upwardly and outwardly from said bottom flat wall, saidholes to facilitate air removal are located at opposite longitudinalextending edge portions of said flat bottom wall adjacent said divergingwalls.
 4. An apparatus for producing grooves in a sheet of plasticcomprising: a supporting bed for receiving said sheet including a heatedportion and an adjacent cooled portion, said bed further including a topsurface with a plurality of ridges and grooves formed on said topsurface extending through the length of said cooled portion and at leastpartially through the length of said heated portion, said bed havingholes extending through said top surface in said grooves to facilitateair removal; heating means operable to controllably heat said heatedportion to maintain said sheet in a soft condition; cooling meansoperable to controllably cool said cooled portion for the cooling andhardening of said sheet; and, air means operable to withdraw air throughsaid holes in said bed creating a vacuum in said grooves of said bedbetween said sheet and said bed forcing said sheet into said grooves ofsaid bed; said ridges having a constant height on said cooled portionand a decreasing height on said heating portion, said heated portionhaving a smooth leading edge portion with said ridges blended smoothlyinto said leading edge portion; said sheet being extruded and conveyedonto said heated portion; said bed including a pair of longitudinallyextending edge portions with said ridges and grooves positionedtherebetween, said edge portions having top surfaces with passagesextending therethrough connected to said air means which is operable towithdraw air through said passages effecting an airtight seal betweensaid edge portions and said sheet moving thereon and further comprising:means operable to contact said sheet and move said sheet along thelength of said bed; said edge portions each having a slot extending thelength thereof and further comprising: a pair Of rollers rotatablymounted over said bed with said rollers each having a circumferentialridge extending into said slot with said sheet forced between eachroller ridge and each slot.